High speed differential relay



y 1934- s. L. GOLDSBOROUGH HIGH SPEED DIFFERENTIAL RELAY Filed Feb. 1,1933 INVENTOR Shirley L. Go ldsboroug/z.

WlT N ESSES:

ATTORNEY Patented May 15, 1934 UNITED STATES PATENT OFFICE HIGH SPEEDDIFFERENTIAL RELAY Shirley L. G-olclsborough, East Grange, N.;J.,assignor to Westinghouse Electric 8 Manufacturing Company, EastPittsburgh, Pa., 2. corporation of Pennsylvania Application February 1,1933, SerialNo.-654,660

13 Claims. 7 (Cl. 175-294) My invention relates to high-speeddifferential relaysandit has particular relation to ratiodiffe'rentialrelays for transformer protection. Suchrelays are made to be assensitive as possible and thus are usually made to respond more'nearlyto a predetermined, departure, from a predetermined normal value,of the ratio of the input current to the output current, rather thanresponding to a predetermined difference between the currentsthemselves. When such relays are utilized to protect certain types ofdevices, notably transformers for power service, false operations arefrequently obtained due to the magnetizing current surge, depending uponthe point in the alternating-current cycle at which the transformer isfirst energized.

It is the object of my invention to provide suitable means forsafeguarding against such faulty operation, in a differential protectivere- 1ay system for a power transformer or the like, without sacrificingeither the high speed or the extreme sensitivity of the balanced-typedifferential relay.

With the foregoing and other objects in View, my invention consists ofthe circuits, apparatus and systems hereinafter described and claimedand illustrated in the accompanying drawing, thefs ingle figure of whichis a diagrammatic View of 'circuits and apparatus embodying myinvention.

"5 A slshown in thedrawing, my invention is utilized for the protectionof a step-up transformer 2 receivingpower from a generator bus 3 andtransmitting power to a transmission line 4 througha circuit breaker 5.The transformer 2 "is protected by a high-speed ratio-(inferentialrelay'6 comprising a balanced beam or armature I carrying a contactmember 8 on one end and a co unterbalancing weight 9 on the other, thecounterbalancing weight being usually adjusted to slightly more thancounterbalance the contact "are energized, in a manner to besubsequently de- "illis energlzedby means of an operating coil member soas'to bias the relay toward its nonactuated position.

The balanced beam or armature '7 is acted uponlby two magnetic circuits11 and 12 which scribedffrom two, current transformers l3 and 14 whichare responsive respectively to the input current and the output currentof the transforinerflto be protected. The magnetic circuit 15whichl isdifferentially excited from the two currenttransformers 13 and 14,whereby an op-v erating force, is developed in order to move the contactmember8 to its actuated position, in. re-

sponse to the difference between the input and output currents of thetransformer 2. The magnetic circuit 12 is energized by two restrainingcoils l6 and 17 which are energized by the currents flowing in thesecondary windings of the respective current transformers '13-and 14.

Under normal conditions, that is, when there is no internal fault in thetransformer 2 to be protected, the two restraining coils 16 and '17 areso. energized that their magnetomotive forces add, so as to normallyprovide a strong restraining force holdingthe contact member 8initsnon-actuated position. shown in the. drawing, the contact member 8is open in its non-actuated condition, and is closed when the relayresponds to a predetermined change in the ratio of input and outputcurrents ofthe transformer 2.

vice which is actuated by current transformers, .it is convenient, whena single device isacted upon by two currents, to assume that eachcurrent flows through the device separately, this assumption beingwarranted because, in any dieffect of the current transformers is to fixthe currents in the-several paths in which they are located. Tracing thecurrents delivered by the two current transformers in the drawing, itwill be noted that the input or primary current I1 of the currenttransfomier 13 passes through the restraining coil 16 and through theturns T1 of the operating coil 15, returning to the current transformerthrough the operating coil 21 of a current-responsive timing device 22to be subsequently described. The outputor secondary current In of themain transformer2 passes through. the timing-element coil 21, throughthe turns T2 of the operating coil 15, and through the restraining coil17. The ampere-turns I1T1 and I2T2 of the primary and secondary currentsin the operating coil 15 are normally equal ,andcopposite in In theparticular relay" In case there is any discrepancy in the" 'videdcircuit including current transformers, the

their effect, so that no pull is produced on the corresponding end ofthe balance beam 7 when there is no fault in the main transformer whichis being protected.

When an internal fault occurs in the transformer being protected, therewill be a decrease in the pull or effectiveness of the restraining coils16 and 17, and at the same time there .willbe a strong flux developed bythe operating coil 15 by 10 reason of the fact that the ampere turnsI1T1 and I2T2 are no longer equal and opposite to each other. It will benoted that, if the fault develops during light-load conditions, therewill be only a very weak restraining force developed by the restrainingcoils 16 and 17, so that the total ef fective ampere-turns on theoperating-coil side, necessary to tip over the balance beam 7, will bemuch less than the effective ampere-turns, or difference in currents,which is necessary to trip 20 the beam when the fault occurs duringheavyload conditions. In this way, the relay responds to ratios ratherthan algebraic differences between currents, thus making the relaysensitive .to small currents as well as large currents. It

will be understood that the moving parts of the relay are made as lightas practicable, in order to obtain substantially instantaneous response.

When a differential relay is made as quick in its action, and assensitive in its operation, as

the relay just described, it will trip, at least occasionally, upon themagnetizing current surges in the transformer 2, lasting for aconsiderable period of time, of the order of a second or more,

.q-after the transformer is first energized. These magnetizing currentsurges start with an initial maximum value, dependent upon the point inthe cycle at which the transformer circuit was closed, and falling off,in accordance with a logarithmic curve, to their final values. If thedifferential relay is very quick and very sensitive, it may,

and frequently does, trip in response to this initial magnetizingcurrent.

In accordance with my invention, I prevent /the possibility of suchfaulty operation of my differential relay by utilizing some sort oflockout device for preventing the differential relay from performing itsnormal tripping function for a certain time after power is first appliedto the main transformer which is being protected. Pref- "erably, forthis purpose, I utilize two timing elements which are indicatedschematically in the drawing, at 22 and 23. The illustration of thetiming elements in the drawing is intended to ,be purely schematic, soas to represent any known type of timing device, such assynchronous-motor devices, induction-motor devices, induction-diskdevices, or solenoid devices operating against a time delay mechanismsuch as the dashpots 24 and 25. The timing mechanisms 22 and 23 areprovided with operating coils 21 and 26, respectively, the former beingenergized in response to current, as previously described, and thelatter being energized in response to the voltage ap- 6 .pearing acrossone of the terminals of the transformer 2 to be protected.

The timing members 22 and 23 are provided with contact devices 2'7 and28 respectively, which are connected in parallel to each other,

'and in series with the control device 8 of the differential relay, sothat the diiferential relay does not become eifective until either oneor both of the timingmembers 22 and 23 have .moved to their actuatedposition. As shownin the drawing, the contact member 8 of the differwillnot close its contacts 27 in response to the ential relay is utilized toenergize the tripping coil 29 of the circuit breaker 5.

Assuming that the generator bus 3 is deenergized and that the maintransformer 2 is disconnected from a live transmission line 4 by meansof th circuit breaker 5, it will be noted that all contacts will beopen. If, now, the circuit breaker 5 is closed, thus energizing themaiii transformer 2, the high-speed differential con tact memberSmayclose substantially instantaneously on the magnetizing surge, but bothof the timer contact members 27 and 28 are open, so that the circuitbreaker 5 is not immediately tripped out. The voltage-responsive timer23 will immediately start to close its contact member 28, and it isgiven such a time delay that, by the time said contact member 28 hasclosed, the diiferential contact member 8 will have reset due to thesubsidence of the surge.

The voltage-responsive timer 23 keeps its contacts closed as long asthere is voltage. If, now, while the main transformer is connected inoperation, an internal fault should develop therein, the fault will, ingeneral, cause a collapse of the voltage applied to thevoltage-responsive 100 timer 23, so that the latter will begin to openits contact member 28; but the quick-acting differential relay 6 is muchfaster, closing its contact member 8 before the trip circuit isopen-circuited at the voltage-timer contact member 28, thus tripping thecircuit breaker 5.

A current-responsive timer, as shown at 22, isf preferably utilizedalso, in addition to the volt age-responsive timer 23, in order toafford pro-. tection in case the main transformer 2 is connected to asource of energy when it has an internal fault somewhere within thetransformer, In such a case, the voltage timer will not operate, becauseof the collapse of voltage caused by the, fault, and I make use of somesort of currentoperated timer to close its contactsand thus trip out thecircuit breaker 5. The current responsive timer 22 can be given a highcurrent, shorttime setting, so that the time necessary to clear, whenclosing in on a faulty transformer, is re duced to a minimum.

I preferably design the current-responsive timer 22 so that it will notclose its contacts in response to the magnetizing current surge in themain transformer 2. This may be done by build 2 ing the timer with acritical-current value so that it will not operate at all, when thecurrent falls below a predetermined minimum value, or so that it willoperate only very slowly when the current falls to a predetermined lowvalue. As above pointed out, the value of the first inrush ofmagnetizing current depends upon the particular point in the cycle atwhich the main transformer; is energized. Calculation and experiencehave shown that this first inrush of magnetizing current may be of thesame order of magnitude as a fault current due to a fault in thetransformer being protected. The magnetizing current falls off, however,very rapidly, ultimately becoming substantially zero, whereas a faultcurrent does' not fall off nearly so rapidly and does not ultimatelybecome substantially zero. It is quite feasible, therefore, in mostinstances, to give the current-responsive timer a setting such that it Pmagnetizing current surge, but so that it will close its contacts 27 inresponse to fault current. Moreover, the current-responsive timer 22 maybe designed so that it will close its contacts 2'? more quickly, inresponse to a fault current, than: 15

1,959,053 the time required for the actuation of the ,voltage-responsive timer -23.

While I have shown my invention in single preferred-form ofembodimentand inasingle application thereof, it willbe obviousthat'manychanges may-be made-by those skilled in the art without departing fromtheessential spirit of. my

and energizing means for adapting it to respond toa predetermineddeparture, from a predetermined normal value, of the ratio of inputcurrent to output current of said transformer, and two timing devices,in combination with means for so correlating said differential relay andsaid timing devices that one of saidtiming devices must be actuatedbefore said differential relay can be effective to perform its relayingfunction, one of said timing devices being a'voltage-responsive timerand the other being a current-responsive timer, and means for energizingsaid timers respectively in accordance with a voltage and a currentderived from said transformer;

2. A differential protective relay system for protecting a powertransformer or the like, comprising a. sensitive high-speed differentialrelay and energizing means for adapting it to respond to the inputcurrent and the output current of said transformer, and twotimingdevices, in combination with means for so'correlating saiddifferential relay and said timing devices that one of said timingdevices must be actuated before said differential relay can beeffectiveto performllits relaying function, one of saidtiming'devicesbeing a voltage-responsive timer and the other being acurrent-responsive timer, and means for energizing said timersrespectively in' accordance with a voltage and a current derivedfrom'said transformer, the current-responsive timer being so designedthat .it will start to move on'some magnetizing current surges in thetransformer,

but will notcomplete such movementmaterially 'before the time requiredby the oltage reSpons'iVe timer, the current-responsivetimer being alsoso I designed that, for any fault-current obtaining'as aresult of afault within the transformer, said current-responsive timer willcomplete its movementbefore the time required by the v'oltageresponsivetimer.

, 3.v A differential .protective relay system for protecting a powertransformer or the like, com-.

prising a sensitive high-speed differential relay andenergizing meansforadapting it to respond to the input current and the output current ofsaid transformer, and two timing devices, in combination with means forso correlating said differential relay and said timing devices that oneof said timing devices must be actuated before said differential relaycan be effective to perform its relaying function, one of said timingdevices being a voltage-responsive timer and the other being acurrent-responsive timer, and means for energizing said timersrespectively in accordance with a voltage and a current derived fromsaid transformer, the current-responsive timer being so designed that itwill start to move on some magnetizing-current surges in thetransformer, but will stop before completing its movement on amagnetizing-current surge.

transformer anda circnit-interr .differentialprotective relay systemcomprising a 4.111 an ele icafs s e a fp a Power er therefo'rfasensitive h h-spee a gre ate? iiiid i i means forf dapt naitto respondto a'predetermineddeparturei from a predterm ne'd inormalvalue, oftheratio of the input 'current'to out- .put current of said transformer,stowageresponsive timingdevice, means for energizing said timingdevic.onUWh t ii'efis riiie .55 energized, saiddilferential relay and saidtiming device each having a contact ele mentfmeans' for actuating saidcircui -i terment, fa 1 gizingcirouitforsaid actuating means,energizing, circuitcomprising thecontac't elementsof both said, relayandsaid timing devicein'series.

5. In an electrical system including a power transformer and acircuit-interrupter therefor," a differential protective relay systemcomprising a sensitive high-speed differential relay'an'd ener- 5 gizingmeans for adapting it to respondto a predetermined departure, from apredetermined normal value, of the ratioof input current :tofoutputcurrent of said transformer, a current responsive timing 'device meansfor energizing said timing 1 00 device in accordance with a currentfunction' or the transformer, said timing device bein g so designed,that' it will start to move on somejm'agnetizing-current surges in thetransformerfbut will ,stopubefore completing its movement on" a. l 05magnetizing-current surge, and means for actu"" ating saidcircuit-interrupter in response totem said relay and saidtiming -device.h

6. In an electrical system including a power transformer and acircuitginterrupter thereforfa differential protective relay systemcomprising a sensitive high-speeddifferential relay andene'rgizing meansfor adaptingit to respond to a predetermined departure, from apredeterminedn ormal value, of the ratio of input current to outputcurrent of said transformer, and two timing de vices, in combinationwith means for so-co rrelating said differential relay and said timingdevices that one of said timing devices must be actuated before saiddifferential relay can be effective to actuate said circuit-interrupter,one ,of said tim ing devices being a voltage-responsive timer and theother being a current responsive timer, and

means for energizing said timers respectively in accordance with avoltage and a current derived from said transformer, saidcurrent-responsive timer operating substantially faster thansaidvoltage-responsive timer on fault-current conditions, Within saidtransformer but not on magnetizing-current surges in said transformer] v'7. In an electrical system including a power" transformer and acircuit-interrupter therefor,

a differential protective relay system comprising a sensitive high-speeddifferential relay and energizing means for adapting it to respond tojthe 5 input current and the output current of said transformer, saidrelay having a contact element adapted to be actuated substantiallyinstantaneously, and two timing devices, in combination with means forso correlating said differential relay and said timing devices that oneof said tim 1' ing devices must be actuated before said differentialrelay can be effective to actuate said circuit-interrupter, each of saidtiming devices having a contact element adapted to be actuated with timerelay, one of said said timing devices being a voltage-responsive timerand the other being a current-responsive timer, and means for energizingsaid timers respectively in accordance with a voltage and a currentderived from i io conditions on the transformer; and thevoltageresponsive timer being adapted to keep its contact element inactuated position for normal voltage conditions on the transformer andto maintain said contact elementin' actuated position,

after collaps er voltage due to a transformer fault; long enough forthesubstantially instantaneously operating differential relay to operate.

' 8. A differential protective relay system for protecting an electricaldevice, comprising a sensitive high-speed differential relay andenergizing means for adapting'it to respond to the input current and theoutput current of said electrical .device, said relay having a contactelement adaptted to be actuated substantially instantaneously,avoltage-responsive timing device, and means for energizing said timingdevice in accordance with a voltage of said device to be protected, incombination with means for so correlatingsaid differential relay andsaid timing device that the latter must be actuated before saiddifferential relay can be effective to perform its relaying function,said voltage-responsive timing device having a contact element adaptedto be actuated with time delay, said voltage-responsive timing devicebeing adapted to keep its contact element in actuated position duringnormal voltage conditions on the device to be protected and to maintainsaid contact element in actuated position,

after collapse of voltage due to an internal fault in the device to beprotected, long enough for the substantially instantaneously operatingdifferential relay to operate.

1 9. The invention as recited in claim 8, in combination with acurrent-responsive timing device operable selectively in response tofault-current conditions in the device to be protected and having acontact element adapted to be actuated faster than said voltage-timercontact element,

in response to said fault-current conditions,and

performing the function described for the voltage-timer contact elementin making said differential relay effective to perform its relayfunction.

' 10. A protective system for a line to be protected, comprising aquick-acting current-responsive differential relay having differentiallyexcited operating windings and additively excited restraining windings,a differentially excited current-responsive timing element, means fordifferentially exciting said operating windings and said timing elementin response to the difference between the currents entering and leavingthe line to be protected, means for additively.

exciting said restraining windings" in response to the sum of thecurrents entering and leaving the line to be protected, and meansresponsiveto an actuation'of said timing element and performing arelaying operation only when said differential relay is also actuated.

11. A protective system for aline to be protected, comprising aquick-acting current-responsive differential relayhaving differentiallyexcitedoperating windings, and two timing devices,

in combination with means for so correlating said sive timer in responseto a voltage function of r the line to be protected. 7

12. A differential protective relay system for protected an electricaldevice, comprising a sensitive high-speed differential relay havingdifferentially excited current-responsive operating windings, excitingmeans therefor responsive differentially to the input current and outputcurrent of said electrical device, and two timing devices, incombination with means for so correlating said diiferential relay andsaid timing devices that one of said timing devices must be actuatedbefore said differential relay can be effective to perform its relayingfunction, one of said timing devices being a voltage-responsive timer,exciting means therefore responsive to a voltage derived from saidelectrical device, and

the other being a differentially excited currentresponsive timer, andexciting means therefor responsive differentially to the input and theoutput current of said electrical device.

13. A differential protective relay system for protecting an electricaldevice, comprising a sensitive high-speed differential relay havingdifferentially excited current-responsive operating windings, excitingmeans therefor responsive dif-. ferentially tothe input current of saidelectrical device, a voltage-responsive timing device, means forenergizing said timing device only when the device to be protected isenergized, means for performing a relaying function in response to bothsaid differential relay and said voltage-respon sive timing device, adifferentially excited current-responsive auxiliary device havingactuating windings, exciting means therefor responsive diiferentially tothe input current and the output current of said electrical device, andmeans for performing a relaying function in response to both saiddifferential relay and said current-responsive auxiliary device.

SHIRLEY L. GOLDSBOROUGH.

